Ballnose end mill

ABSTRACT

The present invention relates to tools for the machining of materials by milling or drilling. The invention provides an improved form for an end mill having a semi-spherical cutting end, or flat cutting end, or drill end the center area of which is configured to better eject chips and thus to improve the surface finish of the metal work piece and tool life. The comprising a body portion to be gripped by a machine tool and a plurality of flutes machined to form a cutting tooth adjacent to the flute, each tooth being provided with a chisel edge, the cutting end being semispherical, or flat, or like drill point and when viewed endwise there being seen a cutting edge starting proximate to the tool center at a position B above the x axis and 0.5A to the right of the y axis.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to tools for the machining of materials bymilling or drilling. More particularly, the invention provides animproved form for an end mill having a semi-spherical cutting end, orflat cutting end, or drill end the center area of which is configured tobetter eject chips and thus to improve the surface finish of the metalwork piece and tool life.

End mills and drills are widely used in milling and drilling operationsdue to their versatile range of application and due to the moderatefirst cost of the tool. End mills and drills are often of cylindricalshape, and are available up to about 80 mm diameter. End mills having asemispherical cutting end (referred to as ball end or ballnose) arewidely used, being particularly useful for CNC work producing complexshapes. End mills with flat cutting end are widely used in ramping,planging and orbital driling and drillind applications. Drills arewidely used in different drilling applications on milling and turningmachines. An end mill typically has 2 to 10 teeth, depending on diametersize and whether intended for rough cutting or finishing. End mills witha flat cutting end used in ramping, planging and orbital driling anddrilling applications typically has 2 to 6 teeth. Drills used indifferent drilling applications on milling and turning machinestypically have 2 to 4 teeth. Teeth are usually of spiral (helical)shape, but can be straight parallel to the axis. Material ofconstruction is high speed steel, solid carbide, cermet or ceramic, orcombinations thereof.

An important problem which has attracted much attention is the clearingaway of the chips produced during machining. Milled and drilling chipsare never continuous and if not removed may again be drawn into thecutting area between one of the cutting teeth and the work piece. Samewith the clearing away of the chips produced during machining is veryimportant in driliing aplications. The result of the not clearing awayof the chips produced during machining is a degraded surface finishmarred by small grooves or scratches, vibration during machining, shorttool life and poor dimensional accuracy. While much can be achieved byimproved coolant flow and by air blasts, an important further factor ineffecting improvement is the shape of the cutting teeth.

Many different cutter forms are seen in the prior art. Among relevantpatents are the following: Japanese application 2001047671 of Takeshi,Japanese patents JP2001334405 and JP2001009524 to Masami, JP2003053617to Takeshi, JP2001341026 to Ryosuke, U.S. Pat. No. 4,934,881 toTsujimura et al., U.S. Pat. No. 5,188,487 to Okawa et al., U.S. Pat. No.5,221,162 to Okawa, U.S. Pat. No. 5,294,219 to Shiratori et al., andU.S. Pat. Nos. 6,231,275 B1 and 6,652,201 B2 to Kunimori et al.

Cutters made according to the Japanese patents. JP2001334405 andJP2001341026 have been found to provide inadequate chip clearancecausing chip reentry and also insufficient access for coolant to thecenter of the end mill.

Unfortunately, without carefully controlled test machining, there is noway of knowing how effective the prior art end mill forms are, merelyfrom the description of the tooth geometry provided. Furthermore, thetooth designs disclosed in the above documents may be optimized formaximum metal removal, or for maximum tool wear life or for resistanceto breakage, or for hard or for soft materials, and the tooth form willvary greatly as a function of the different design parameters, and ofthe cutter diameter.

Extensive experience with various prior-art cutters has howeverindicated the continued existence of surface flaws in work piecesmachined by prior art ballnose end mills, and the root of the problemhas been traced to chips which were not dispersed by the coolant andwhich reentered the cutting area and in the course of machining lodgedmomentarily between the end mill and the work piece.

OBJECTS OF THE INVENTION

It is therefore one of the objects of the present invention to obviatethe disadvantages of prior art ballnose end mills and drills and toprovide a design which improves dispersal of the chip out of the cuttingarea without diminish other properties of the end mill or drill.

It is a further object of the present invention to thereby improvesurface finish of the work piece, reduce tool vibration and extend toollife.

SUMMARY OF THE INVENTION

The present invention achieves the above objects by providing a ballnoseend mill, end mills with flat cutting end used in ramping, planging andorbital driling and drilling applications and drills of diameter Dconfigured for improved chip removal, comprising a body portion to begripped by a machine tool and a plurality of flutes machined to form acutting tooth adjacent to said flute, each tooth being provided with achisel edge, the cutting end being semispherical, or flat, or like drillpoint and when viewed endwise there being seen a cutting edge startingproximate to the tool center at a position B above the x axis and 0.5Ato the right of the y axis, said cutting edge extending at an angle arelative to the y axis for a length C, value of A, being the totaloff-set between cutting edges of two teeth disposed at 180° to eachother, for the machining of different materials is 0.003D to 0.030D,both B and C having lengths of between 0.3A to 10.5A, and the angle ahaving a value of between 50-450.

PREFERRED EMBODIMENT OF THE INVENTION

In a preferred embodiment of the present invention there is provided aballnose end mill, or flat end mill, or drill wherein said cutting edgestarting at position B is curved at a radius R, the locus of said radiusbeing at its right side when viewing the upper tooth of thesemi-spherical end, or flat end mill, or drill and the value of R is0.5A−5A.

The present inventors have prepared a 16 mm diameter two-flute ballnoseend mill which was optimized for use on hard materials, coated TiAlN.The end mill was manufactured according to the present specification andproduced a smooth surface free from the characteristic flaws resultingfrom faulty chip clearing.

-   Cutting conditions: Material Steel D2 hardened to 60-62 HRc,-   Cutting speed—150 m/min, cutting feed—0.08 mm/teeth, Axial depth of    cut—0.3 mm,-   Radial depth of cut—0.3 mm, dry cutting.-   Test results: tool life 200 m in material, surface finish 8-12 micro    inch.

SHORT DESCRIPTION OF THE DRAWINGS

The invention will now be described further with reference to theaccompanying drawings, which represent by example preferred embodimentsof the invention. Structural details are shown only as far as necessaryfor a fundamental understanding thereof. The described examples,together with the drawings, will make apparent to those skilled in theart how further forms of the invention may be realized.

In the drawings:

FIG. 1 is an elevational view of a prior-art ballnose end mill;

FIG. 1 a an elevational view of a prior-art flat end mill;

FIG. 1 b an elevational view of a prior-art drill.

FIG. 2 is an end view of the prior art ballnose end mill seen in FIG. 1;

FIG. 2 a is an end view of the prior art flat end mill-seen in FIG. 1 a;

FIG. 2 b is an end view of the prior art drill seen in FIG. 1 b;

FIG. 3 is an enlarged view of the center portion of a prior-art ballnoseend mill FIG. 2;

FIG. 4 is an end view of a further prior-art ballnose end mill;

FIG. 5 is an enlarged view of the center portion of FIG. 4;

FIG. 6 is an end view of an ballnose end mill according to the presentinvention;

FIG. 6 a is an end view of an flat end mill according to the presentinvention;

FIG. 6 b is an end view of an drill according to the present invention;

FIG. 7 is a an enlarged view of the center portion of FIG. 6; FIG. 6 a;FIG. 6 b;

FIG. 8 is an end view of a further embodiment of the ballnose end millaccording to the present invention;

FIG. 8 a is an end view of an flat end mill according to the presentinvention;

FIG. 8 b is an end view of an drill according to the present invention;and

FIG. 9 is an enlarged view of the center portion of FIG. 8, FIG. 8 a;FIG. 8 b;

FULL DESCRIPTION OF THE INVENTION

There is seen in FIGS. 1 to 3 a prior-art 2-flute helical ballnose endmill 10, which corresponds to Japanese patents nos. JP2001334405 andJP2001341026. In FIGS. 1 a and 2 a there is seen a prior art 2 flutehelical flat end mill while FIGS. 1 b and 2 b illustrate a prior art 2flute helical drill. The tools 10, 10 a and 10 b have a shank portion 12and tooth flanks 14 capped by a cutting edge 16.

The cutting edge 16 of the cutter in FIG. 2, 2 a and 2 b and againgreatly enlarged in FIG. 3 carries around the hemispherical end with anoff-set A. The width of the chisel edge 18 is between 0.01-0.20 mm.

The chisel edge angle relative to the cutting edge is 165-185°, soaccordingly the chisel edge can be in line with the cutting edge. Thelength L of the chisel edge 18 is between 3-7 times that of the chiselwidth.

A slightly different version of an end mill 20 is seen in FIGS. 4 and 5.The offset distance A is between 0.05 and 0.40 mm and again the chiseledge angle is 165-185°

Referring now to FIGS. 6, 6 a, 6 b and 7, there is seen a ballnose endmill 22, a flat end mill 22 a and a drill 22 b of diameter D accordingto the present invention. The end mill 22, the flat end mill 22 a andthe drill 22 b are configured for improved chip removal, and comprises abody portion 12, seen in FIG. 1, FIG. 1 a, FIG. 1 b to be gripped by amachine tool and two flutes 26 machined to form a cutting tooth 24adjacent to the flute 26. Each tooth 24 is provided with a cutting edge28, which continue, with a side-to-side changeover at the center.

Viewings the end mill 22, the flat end mill 22 a and the drill 22 bendwise there is seen a tooth-end cutting edge 32 starting proximate tothe cutter center 34 at a distance B above the x axis and a distance0.5A to the right of the y axis. The tooth end cutting edge 32 extendsat an angle a relative to the y axis for a length C.

The following values are typical for a ballnose end mill intended foruse for the machining of hard materials: $\begin{matrix}{A = {{the}\quad{total}\quad{off}\text{-}{set}\quad{between}\quad{cutting}\quad{edges}\quad{of}\quad{two}\quad{teeth}}} \\{{disposed}\quad{at}\quad 180{^\circ}\quad{to}\quad{each}\quad{other}} \\{= {0.003D\quad{to}\quad 0.030{D.}}}\end{matrix}$

-   B=between 0.3A to 1.5A.-   C also=between 0.3A to 1.5A, but can be different from B.-   Angle a=5° to 45°.

Considering an end mill D=16 mm diameter for hard steels, typical valuesare as follows:

-   A=0.2 mm-   B=0.1 mm-   C=0.25 mm-   a=35°

Turning now to FIG. 8, FIG. 8 a, FIGS. 8 b and 9, there is depicted afurther embodiment of a ballnose end mill 36, a flat end mill 36 a, anda drill 36 b also according to the present invention. A tooth-endcutting edge 38, is seen starting at a distance B above the x axis and adistance 0.5A to the right of the y axis, as seen in FIG. 7. However theedge 38 is curved at a radius R. The locus of the radius R is to theright of the y axis when viewing the upper tooth 28 of the tools. Usingthe x-y coordinates, the locus is at y=B and x=0.5A+R

The value of R is 0.5A-5A, which in the given example where D=16 thenR=about 0.4 mm.

For both brevity and clarity the examples illustrated have only 2flutes. The same geometry is however equally applicable to larger toolshaving 4, 6, 8 or 10 flutes.

The scope of the described invention is intended tb include allembodiments coming within the meaning of the following claims. Theforegoing examples illustrate useful forms of the invention, but are notto be considered as limiting its scope, as those skilled in the art willreadily be aware that additional variants and modifications of theinvention can be formulated without departing from the meaning of thefollowing claims.

1. A tool such as a ballnose end mill, or flat end mill, or drill ofdiameter D configured for improved chip removal, comprising a bodyportion to be gripped by a machine tool and a plurality of flutesmachined to form a cutting tooth adjacent to said flute, each toothbeing provided with a chisel edge, the cutting end being semispherical,or flat, or like drill point and when viewed endwise there being seen acutting edge starting proximate to the cutter center at a position Babove the x axis and 0.5A to the right of the y axis, said cutting edgeextending at an angle a relative to the y axis for a length C, value ofA, being the total off-set between cutting edges of two teeth disposedat 180° to each other, for the machining of different materials is0.003D to 0.030D, both B and C having lengths of between 0.3A to 1.5A,and the angle a having a value of between 5°-45°.
 2. The tool as claimedin claim 1, wherein said cutting edge starting at position B is curvedat a radius R, the locus of said radius being at its right side whenviewing the upper tooth of the tool's end, and the value of R is0.5A-5A.
 3. A ballnose end mill, or flat end mill, or drill configuredfor improved chip removal, substantially as described hereinbefore andwith reference to the accompanying drawings.